Capacitors used in certain applications, particularly within the automotive, aerospace and oil and gas industries might routinely be exposed to temperatures of up to 200° C. The capacitance of conventional capacitors varies considerably with temperature, rendering them unsuitable for use in high temperature environments. It is therefore desirable to provide a capacitor with improved high temperature performance.
Capacitance may also vary with the applied voltage. For example, a conventional capacitor with a nominal capacitance of 100 nF may in fact operate at only 20 nF when a voltage is applied. It is desirable to provide a capacitor with reduced sensitivity to the effects of the applied voltage.
Low dissipation factor (or loss) is a useful characteristic for capacitors, particularly when used for AC applications. This property has however generally been restricted to low capacitance COG type capacitors and has not been available in a higher capacitance X7R or X8R ranges.
Various attempts have been made to provide capacitors with improved performance at high temperature.
International Patent Application Publication No. WO2013/144637 provides a high capacity capacitor which includes a spacer element formed of a high energy density dielectric material. The dielectric material comprises doped bismuth ferrite. The doping agent includes strontium and titanium. The doping agent has the effect of increasing the difference between the saturation polarisation and the remnant polarisation of bismuth ferrite as well as reducing charge leakage, making bismuth ferrite a suitable material for a high energy density capacitor. The doped bismuth ferrite exhibits good temperature stability.
Various attempts have also been made to improve the reliability of conventional capacitors.
International Patent Application Publication No. WO2013/186172 provides a capacitive structure comprising first and second components, at least one component comprising a plurality of capacitive layers of a dielectric, each layer arranged between electrodes of different polarity, wherein the first and second components are arranged in a stack separated by a stress reducing layer having a supporting structure with an open mesh in which air acts to reduce the transmissibility of cracks through the stress reducing layer.
The present invention aims to provide a capacitor with improved efficiency, lower loss and a smaller sensitivity to temperature and the applied voltage.